In transportation equipment such as automotive vehicles and motorcycles, a suspension device is interposed between a vehicle body and a wheel. The suspension device suppresses the transmission of an impact due to the unevenness of a road surface to the vehicle body.
JP9-217780A discloses a front fork as a suspension device for suspending a front wheel of a motorcycle. This suspension device is an upright suspension device and includes a suspension device main body F composed of an outer tube 1 which is to be coupled to a wheel side and an inner tube 2 which is to be coupled to a vehicle body side and a tip side of which is retractably inserted into the outer tube 1 as shown in FIG. 6.
The suspension device includes a hollow pipe 10 a base end side of which is coupled to the outer tube 1 and a tip side of which enters and exits from the inner tube 2 as the suspension device main body F extends and contracts, a partition wall body 100 which is held on the outer periphery of a tip part of the hollow pipe 10 and slides in contact with the inner peripheral surface of the inner tube 2, and a piston 200 which is held on the inner periphery of a tip part of the inner tube 2 and slides in contact with the outer peripheral surface of the hollow pipe 10.
The partition wall body 100 partitions the outside of the hollow pipe 10 into a working chamber (not shown) which is formed on the outer periphery of the hollow pipe 10 and filled with working fluid and a reservoir R which is formed inside and above the hollow pipe 10 and in which the working fluid and gas are stored. The piston 200 partitions the working chamber into an extension-side chamber A on the inner tube side (upper side in FIG. 6) and a contraction-side chamber B. The extension-side chamber A communicates with the reservoir R via a damping flow passage M1 formed by an orifice perforated on the tip side (upper side in FIG. 6) of the hollow pipe 10. The contraction-side chamber B communicates with the reservoir R via a hole 31 perforated on the base end side (lower side in FIG. 6) of the hollow pipe 10.
The partition wall body 100 and the piston 200 are each formed into an annular shape and mounted movably in an axial direction. A first flow passage L1 allowing communication between the reservoir R and the extension-side chamber A is provided on the inner periphery of the partition wall body 100. A second flow passage L2 allowing communication between the extension-side chamber A and the contraction-side chamber B is provided on the outer periphery of the piston 200.
A cut 101 is formed along a radial direction on an extension-side chamber side surface (lower surface in FIG. 6) of the partition wall body 100. Accordingly, the partition wall body 100 functions as a first check valve V1 for permitting the working fluid passing in the first flow passage L1 to move only from the reservoir R to the extension-side chamber A. On the other hand, a cut 201 is formed along a radial direction on an extension-side chamber side surface (upper surface in FIG. 6) of the piston 200. Accordingly, the piston 200 functions as a second check valve V2 for permitting the working fluid passing in the second flow passage L2 to move only from the contraction-side chamber B to the extension-side chamber A.
When the suspension device extends, the extension-side chamber A is pressurized and the contraction-side chamber B is depressurized by the piston 200. At this time, communication between the first and second flow passages L1, L2 is blocked by the partition wall body 100 functioning as the first check valve V1 and the piston 200 functioning as the second check valve V2. Thus, the working fluid in the extension-side chamber A flows out to the reservoir R through the damping flow passage M1 of the hollow pipe 10 and the working fluid in the reservoir R flows into the contraction-side chamber B through the communication hole 31.
When the suspension device contracts, the contraction-side chamber B is pressurized and the extension-side chamber A is depressurized by the piston 200. At this time, the communication between the first and second flow passages L1, L2 is permitted by the partition wall body 100 functioning as the first check valve V1 and the piston 200 functioning as the second check valve V2. Thus, the working fluid in the contraction-side chamber B flows out to the reservoir R and the extension-side chamber A through the communication hole 31 of the hollow pipe 10 and second flow passage L2, and the working fluid in the reservoir R flows into the extension-side chamber A through the first flow passage L1 and the damping flow passage M1.
Accordingly, the suspension device generates a damping force due to resistance produced when the working fluid passes through the first flow passage L1, the second flow passage L2, the damping flow passage M1 and the communication hole 31 as the suspension device main body F extends and contracts. Further, an extension-side damping force which is a damping force when the suspension device extends is larger as compared with a contraction-side damping force which is a damping force when the suspension device contracts.
Further, in the above suspension device, the partition wall body 100 partitioning between the reservoir R and the extension-side chamber A and the piston 200 partitioning between the extension-side chamber A and the contraction-side chamber B are arranged between the inner periphery of the inner tube 2 and the outer periphery of the hollow pipe 10 and each formed into an annular shape. Since the partition wall body 100 and the piston 200 are mounted movably in the axial direction and function as the first and second check valves V1, V2 by each including the cut 101, 201 on one surface, a leaf valve can be eliminated.
Thus, the above suspension device can be easily assembled and inexpensively manufactured as compared with a suspension device for generating a damping force utilizing a deflection characteristic of a leaf valve.